1. Field of the Invention
This invention relates to methods of associating I/O paths in varied groupings with central processing systems and shared peripheral devices, and methods for modifying such groupings while associated devices have reserve affiliations or allegiances which normally would be capable of blocking such modifications.
2. Background Prior Art & Problems Solved by the Invention
In their U.S. Pat. No. 4,207,609 supra, Luiz et al have disclosed a method for associating varied I/O path groups with central processing units (CPUs) and shared-access devices whereby CPUs and devices can communicate on a so-called "path-independent" basis. In such communications a CPU and associated I/O channel may initiate contact with a device via one path in an associated path group, then disconnect from the device (while the device "asynchronously" performs a required task, and the channel is free to perform other unrelated tasks), thereafter reconnect, at the initiative of the device, via the same or another channel and via the same or another path in the path group, and thereafter continue to perform an operation designated during the original connection.
Commands SHID (Set Host Identity) and SNID (Sense Host ID) disclosed by Luiz et al, for respectively creating such path group associations and interrogating associational states of paths, require "unique" identification of CPUs which issue these commands. However, this poses a problem when applying these commands relative to so-called "non-static" multiprocessing (MP) systems which are dynamically configurable to incorporate variable numbers of CPUs and thereby may have time-varying identities.
The SHID command as defined by Luiz et al is useful for establishing a path group, deleting (resigning) a path from an established group, and cancelling (disbanding) an established group. But the patent does not indicate specifically how such commands may be utilized relative to devices having conflicting reserve affiliations or other "allegiances" (to other systems and/or paths) which may delay the processing of such commands (until the affiliation or allegiance has been released). In certain situations this requirement for delaying path grouping operations until affiliations or allegiances have been released may impose undesirable overhead costs (e.g. for communicating with other systems having shared access to the device).
In accordance with the method disclosed by Luiz et al path map tables constructed and referenced by device control units (CUs) indicate identities of CPUs associated with specific CU ports (i.e. paths), path groupings relative to such CPUs, and device allegiances or affiliations relative to such paths and CPUs. However, beyond the disclosure of Luiz et al there exists presently a need for allowing CUs to be able to differentiate between CPUs which can only initiate operations in a path-independent mode and CPUS which can both initiate operations and respond to device-initiated communications (e.g. "requests for reconnection", "no longer busy" status indications, and "asynchronous event" status indications) in a path-independent mode.
Luiz et al also refer to a path state sensing command SNID (Sense Host Identity) for enabling host systems to interrogate path states in respect to membership in path groups. However, there exists presently a need for enabling host system to obtain additional device/path state information which could considerably enhance the effectiveness of path group utilization.